Tarti shma mina

The gemara in nida 57b says there are three drashos that we need to learn from "bivsara": 1. that she's temeia even before the dam actually comes out 2. that if the blood comes out inside of something else she's not temeia and 3. she's not temeia if she didn't have a hargasha. The gemara says that one drasha is from basar, another is from bivsara and "tarti shma mina." There are two ways to understand that line. One is that the first two drashos could be made from one extra thing because they're both teaching that she's temeia when it touches her flesh - that could be a chumra (she's temeia before it actually comes out) or a kula (she's not temeia if it comes out inside of something else). Then we're left with another drasha to teach that she must have a hargasha. Others (Ran) learn that there are actually three drashos - the beis at the beginning, the hay at the end and the word itself. It doesn't sound like it from our gemara which says that it could have said b'basar but the bivsara is extra implying that the beis at the beginning is not extra. However, someone pointed out this morning at the daf that there are different girsaos on daf 21 about what is extra so it is definitely possible to learn that there are three extra things here.